Interpretive Summary: Approaches to molecular systematics are becoming central to understanding the patterns and distribution of biodiversity for parasite faunas in vertebrate hosts. Promoted is a clear definition of species associations and the historical and contemporary factors that have served as determinants or drivers for distribution. In further tests of these approaches we explored the distribution of nematode parasites in furbearing hosts from North America and eastern Siberia, contributing to a broader knowledge of the physical and biotic processes that have served to structure the North American fauna. The nematode Soboliphyme baturini was found to represent a single species with relatively broad geographic range across Beringia and northwestern North America, based on assessment of molecular sequence data for adult and juvenile parasites. Refuted are hypotheses suggesting that several cryptic species are partitioned either among an array of mustelid definitive hosts or across the vast region that links North America and Eurasia. Host specificity for this species is examined based on a comprehensive list for definitive hosts, derived from new field surveys and existing literature for S. baturini. Only 5 mustelids (Gulo gulo, Martes americana, M. caurina, M. zibellina and Neovison vison) appear to have significant roles in the life history, persistence and transmission of this nematode. Soboliphyme baturini readily switches among M. caurina, M. erminea, or N. vison at any particular locality throughout its geographic range in North America. The life cycle of S. baturini is explored through a review of diet literature for two marten species, M. americana and M. caurina. Shrews (Soricomorphs: Soricidae) comprise >8% of prey for these mustelids suggesting their putative role as paratenic hosts. Juvenile nematodes found in the diaphragms of soricids are genetically identical to adult S. baturini found in the stomachs of mustelids at the same locations in both Asia and North America corroborating a role in transmission for species of Sorex. New data and interpretations on the distribution of nematode pathogens in wildlife species emanate from these studies. Significantly, establishing the roles for each participant (host) in a parasite’s life cycle is essential to interpreting ecology, epidemiology, distribution and phylogeographic history, which provide baselines for documenting the influence of ongoing environmental perturbation.

Technical Abstract:
The nematode Soboliphyme baturini Petrov, 1930 was found to represent a single species with relatively broad geographic range across Beringia and northwestern North America, based on assessment of molecular sequence data for adult and juvenile parasites. Refuted are hypotheses suggesting that several cryptic species are partitioned either among an array of mustelid definitive hosts or across the vast region that links North America and Eurasia. Host specificity for this species is examined based on a comprehensive list for definitive hosts, derived from new field surveys and existing literature for S. baturini. Only 5 mustelids (Gulo gulo, Martes americana, M. caurina, M. zibellina and Neovison vison) appear to have significant roles in the life history, persistence and transmission of this nematode. Soboliphyme baturini readily switches among M. caurina, M. erminea, or N. vison at any particular locality throughout its geographic range in North America. The life cycle of S. baturini is explored through a review of diet literature for two marten species, M. americana and M. caurina. Shrews (Soricomorphs: Soricidae) comprise >8% of prey for these mustelids suggesting their putative role as paratenic hosts. Juvenile nematodes found in the diaphragms of soricids are genetically identical to adult S. baturini found in the stomachs of mustelids at the same locations in both Asia and North America corroborating a role in transmission for species of Sorex.